The Analgesic Effects of Different Extracts of Aerial Parts of Coriandrum Sativum in Mice

Regarding the effects of Coriandrum sativum (C. sativum) on central nervous system, in the present study analgesic properties of different extracts of C. sativum aerial partswere investigated. The mice were treated by saline, morphine, three doses (20, 100 and 500 mg/kg) of aqueous, ethanolic, choloroformic extracts of C. sativum and one dose (100 mg/kg) of aqueous, two doses of ethanolic (100 and 500 mg/kg) and one dose of choloroformic (20 mg/kg) extracts of C. sativum pretreated by naloxone. Recording of the hot plate test was performed 10 min before injection of the drugs as a base and it was consequently repeated every 10 minutes after the extracts injection. The maximal percent effect (MPE) in the groups treated by three doses of aqueous, ethanolic and chloroformic extracts were significantly higher than saline group which were comparable to the effect of morphine. The effects of most effective doses of extracts were reversed by naloxone. The results of present study showed analgesic effect of aqueous, ethanolic and chloroformic extracts of C. sativum extract. These effects of the extracts may be mediated by opioid system. However, more investigations are needed to elucidate the exact responsible mechanism(s) and the effective compound(s).


INtrODUctION
Pain is an unpleasant sensation which is elicited by damaging or potentially damaging noxious stimuli. Several factors including sociocultural, psychological and biological conditions have important roles in pain perception (1)(2)(3). Pain relief can be achieved by nonpharmacologic approaches or by administration of a diversity of drugs. Analgesic drugs are used in single or in combination to affect peripheral or central nervous system (CNS) to decrease pain sensation (4). At present, the most widely used ORIGINAL ARTICLE medications for management of pain are acetaminophen, opioids, and nonsteroidal anti-inflammatory agents. However, the clinical uses of these drugs are accompanied with unpleasant side effects such as hepatic failure, gastrointestinal events, renal dysfunction, respiratory depression, and addiction (5). Therefore, the search for new analgesic agents with lesser side effects and more efficacies is of great interest.
Medicinal plants have been repeatedly considered as one of the main sources of medicines for treatment of several health problems of human. They are widely used to treat a wide range of CNS disorders including neurodegenerative diseases, stroke, dementia, seizures and insomnia (6)(7)(8)(9)(10).
Coriandrum sativum (C. sativum) is an annual herb belonging to the Apiaceae family. It is also known as coriander, cilantro, Arab parsley, Chinese parsley and Dhania (11). Although, all parts of the plant are edible, its fresh leaves and dried seeds are most frequently used in many cultures. C. sativum is widely used in traditional medicine to treat anxiety, dizziness, headache, edema, fever, digestive disorders, respiratory diseases, allergies, and burns (12).
In our previous work, it was found that aerial parts of this plant bearing compounds which show sedative/hypnotic effects in mice (13). Also, Emamghoreishi and colleagues reported that aqueous extract of C. sativum seed has anxiolytic and muscle relaxant effects (11). Considering these effects of C. sativum on nervous system, we aimed to test the possible analgesic effects of different extract of C. sativum.

Drugs and chemicals
Morphine and naloxone was purchased from Temad Company (IRAN). Chloroform (99.8%) and ethanol (96%) were obtained from Merck Company.

Animal groups
In this study, 120 virgin male mice (27-32 g in weight) were used. The animals were maintained at the animal house under controlled conditions including 12 h light and dark cycle, 22-24 o C temperature and appropriate humidity with laboratory chow and water provided ad libitum. The study protocol using the laboratory rats complied with the general guidelines of the animal care of Mashhad University of Medical Sciences, Iran. The animals were divided into 15 groups (n=8 in each group)and treated as follows: (group1) saline as control group, (group 2) morphine (10 mg/kg), (groups 3-5) three doses of aqueous extract of C. sativum (20, 100 and 500 mg/kg), (groups 6-8) three doses of ethanolic extract of C. sativum (20, 100 and 500 mg/ kg), (groups 9-11) three doses of chloroformic extract of C. sativum (20, 100 and 500 mg/kg), (group 12) 100 mg/kg aqueous extract pretreated by naloxone (4 mg/kg), (groups 13-14) two doses of ethanolic extract (100 and 500 mg/kg) pretreated by naloxone (4 mg/kg) and (group 15) 20 mg/kg of choloroformic extract of C. sativum extract pretreated by naloxone ( 4 mg/kg).

Plant extracts
The aerial parts (leaves, stems, twigs) of C. sativum were collected from Neyshabur area, (Razavi Khorasan state, Iran). The identity of the plant was confirmed and for future reference a voucher specimen (10068) was deposited at the herbarium of school of Pharmacy (Mashhad University of Medical Sciences, Iran). The plant aerial parts were air-dried under shade at room temperature. Then, the dried aerial parts (50 g) were chopped, finely grounded, and extracted using a Soxhlet apparatus. Duration of extraction was 48 hours and 300 ml of distilled water, ethanol, or chloroform were used as solvent to prepare aqueous, ethanolic and chloroformic extracts, respectively (24)(25)(26). The extracts reduced to dryness with a rotary vacuum evaporator. The yields of aqueous, ethanolic and chloroformic extracts were 15%,17% and 5% respectively.

Nociceptive test
To assess nociceptive responses, hot plate method was used. The mice were placed on the hot plate with temperature setting controlled at 55 ± 0.2 o C. Cut-off time was 60 s. Nociceptive response was defined as licking forepaws or moving hind paws. Time duration between placing the animals on hot plate and licking fore paws or moving hind paws was considered as the reaction time. The hot plate test was performed as a base record 10 min before injection of the drugs and consequently it was repeated 5 times, every

statistical analysis
All data were expressed as Mean ± SEM and analyzed by using ANOVA followed by Tukey's post hoc comparison test. P values less than 0.05 were considered to be statistically significant.

Analgesic activity of aqueous extract
The results showed that MPE in the animals treated by 20 mg/kg of aqueous extract was significantly higher than that of control group at 30 and 50 min after injection of the extract (P<0.05-P<0.01). Treatment of the animals by 100 mg/kg of the extract also increased MPE at10, 20, 30, 40 and 50 min compared to vehicle treated animals (P<0.05-P<0.001). MPE in animals treated by 500 mg/kg of the aqueous extract was higher than that of control only at 30 min after administration (P<0.01). Morphine administration increased MPE at all times after injection (P<0.001) (Fig. 1).

Analgesic activity of ethanolic extract
The results showed that MPE in the group treated by 20 mg/kg of ethanolic extract was significantly higher than that of control group at all times after injection of the extract (P<0.01-P<0.001). Treatment of the animals by 100 mg/kg of the extract also increased MPE at all times compared to vehicle treated animals (all P<0.001). MPE in animals treated by 500 mg/kg of the ethanolic extract was higher than that of control at 10-50 min after administration (P<0.01-P<0.001). Morphine administration increased MPE at all times after injection (P<0.001) (Fig. 2).

Analgesic activity of chloroformic extract
The results showed that MPE in the animal group treated by 20 mg/kg of chloroformic extract was significantly higher than that of control group all times after injection of the extract (P<0.01-P<0.001). Treatment of the animals by 100 mg/kg of the extract also increased MPE at 30, 40 and 50 min after injection compared to vehicle treated animals (P<0.01-P<0.001). MPE in animals treated by 500 mg/kg of the aqueous extract was higher than that of control at 10-50 min after administration (P<0.05-P<0.001). Morphine administration increased MPE at all times after injection (P<0.01-P<0.001) (Fig. 3).

Effect of naloxone on analgesic activity of the extracts
Pretreatment by naloxone reduced analgesic effect of 100 mg/kg of aqueous extract at 20 and 50 min (P<0.05-P<0.01, respectively) (Fig. 4). MPE of the animals pre- treated by naloxone before 100 mg/kg of the extract was significantly lower than that of animals treated only by 100 mg/kg of the extract at all times (P<0.05-P<0.01). The results also showed that naloxone reduced the analgesic activity of 500 mg/kg of the ethanolic extract at 10 and 50 min (both P<0.01) (Fig. 5). As the Figure 6 shows the MPE of the animals treated by naloxone before 20 mg/ kg of chloroformic extract was significantly lower than that of the animals treated by only 20 mg/kg of the extract (P<0.05-P<0.001).

DIscUssION
The results of present study showed that three extracts (aqueous, ethanolic and chloroformic) of aerial parts of C. sativum had analgesic effects. The analgesic effect of the extracts was comparable to morphine and was attenuated by naloxone pretreatment. Consistent with this finding, it was previously shown that percolated methanolic extract of C. sativum had analgesic effect which was reversible by naloxone (30). In another study analgesic effects of the aqueous extract of the seeds of C. sativum had been reported using hot plate and tail flick tests (31). Because aerial parts of C. sativum are widely consumed as vegetable all over the world and no pharmacological studies have been yet evaluated the analgesic activity of different extracts of these parts of the plant, by evaluating we showed that C. sativum aerial parts had analgesic effects. The effects of ethanolic and chloroformic extracts were higher than aqueous extract; therefore it seems that the compounds that are soluble in ethanol or chloroform have potent analgesic effects.
The chemical compound(s) responsible for the analgesic effect of the extracts which didn't identify in the present study and need to be future studies. However, the presence of the flavonoids such as quercitin has been reported (32). It has been shown that the flavonoids have considerable anticonvulsant and analgesic effects (33)(34)(35). Sedative, CNS depressant and analgesic effects of falvonoids such as quercetin has been attributed to the affinity for the central benzodiazepine receptors (33,34,(36)(37)(38)(39)(40). The beneficial effect of linalool in pentylenetetrazole seizure models as well its analgesic effects has been suggested (41,42). It might be suggested that the beneficial effects of the extracts which were observed in the present study are at least in part due to linalool which is a main compound in coriander (43). Analgesic effects of polyphenols including rutin, caffeic acid, and gallic acid has also been reported which can be isolated from C. sativum (9,(44)(45)(46)(47)(48)(49).
In conclusion, the present data, for the first time, demonstrated that different extracts from C. sativum aerial parts have analgesic activities. These activities were reversed be naloxone therefore; the interaction with opioid system might be suggested. Isolation of the active compound(s) from the extract may yield novel analgesic agent.

cONFLIct OF INtErEst
We declare that we have no conflict of interest.